This invention relates generally to an apparatus and method for decorating articles and more specifically an apparatus wherein the articles are each carried by a respective article carrier which is passed through the apparatus by a conveyor means with a stepwise motion on a circulatory conveyor path along a guide track, each article being released from its carrier after passing at least one treatment station.
Decoration includes for example applying printing, colouring, a label or the like to an article, or treating an article at its surface to produce a desired effect thereat.
In one form of apparatus for decorating articles by a screen printing process (specification U.S. Pat. No. 2,881,699) a continuously circulating conveyor means in the form of a chain carries entrainment members which are positively or form-lockingly connected to the article holders. The article holders are transported along a circulatory conveyor path, the course of which corresponds to that of the conveyor chain, continuously over the major part of the extent thereof. It is only in the region of the screen printing station that the article holders and therewith also the articles carried thereby are transported with a stepwise motion, for the purpose of permitting the articles, which are of non-round cross-section, to be printed therearound. The stepwise forward conveying movement of the article holders in the printing station is achieved by virtue of the entrainment members which remain permanently in engagement with the article holders performing a relative movement with respect to the article holders along curve-like surfaces on the article holders. The use of a continuously moving conveyor means means that this known apparatus which in addition only provides one treatment station in the form of a screen printing station is subject to certain limitations in regard to the utility thereof. Due to the circulating conveyor means, the speed of conveying movement and the residence time in the printing station are fixed within narrow limits. Although it is possible to vary the speed of conveying movement and also the residence time in the treatment station, within certain limits, by suitable design in respect of the article holder curve or cam surfaces that co-operate with the entrainment members, nonetheless that involves a very high level of expenditure as all article holders must be suitably constructed at their curve or cam surfaces which co-operate with the entrainment members. The degree of freedom is also restricted by virtue of the fact that the configuration of the curve or cam members is linked to the cross-sectional shape of the article to be printed. There is no possibility of any alterations in the mode of operation of this known apparatus, for example in regard to different residence times in given treatment stations. In addition, the stepwise conveying movement of the articles is tied in to the non-round cross-sectional shape thereof.
German laid-open application (DE-OS) No. 24 02 836 and specification U.S. Pat. No. 4,005,649 disclose a screen printing apparatus having a plurality of treatment stations, in which there is also a continuously circulating conveyor means in the form of a chain, to which the article carriers are fixedly mounted. In that arrangement, the article or object to be printed is embraced by one of the article carriers when the article moves into the machine, and is transported by that carrier through the entire machine, that is to say, through all the treatment stations therein. The advantage of that known apparatus is that, once the article to be printed has been engaged by an article carrier, it remains in its relative position with respect thereto. In that way, it is readily possible to provide that the article, from the outset, occupies a given position in the individual printing stations, and in particular a given angular position in relation to the respective printing means, so that there is no need for any special arrangement for specifically aligning the article with respect to each printing means. On the other hand, with that known apparatus, there is no possibility of the article being allowed to stay in given stations for a longer period than in other stations. That means that the apparatus is less suitable for example for printing on articles comprising plastics as in that respect it is always necessary for the print applied in the respective last station to be allowed to dry before the next printing operation can be carried out. Under the circumstances involved here, the arrangement of drying stations of that kind would mean that the known apparatus would be very long.
The last-mentioned problem is avoided in a screen printing machine which is disclosed in German laid-open application (DE-OS) No. 25 30 360 and specification U.S. Pat. No. 4,048,914, as the latter is provided with a plurality of reciprocably movable article carriers which are connected fixedly to the drive means, and the article, in the course of its being conveyed through the machine, is freed by an article carrier and picked up again by the following article carrier. That stepwise conveying movement affords the possibility of taking account of certain requirements in regard to residence time in the individual stations, for example in such a way that the operation of printing on the articles is carried out during a step in the conveying movement and the subsequent operation of drying the print on the article is performed in a station in which the article remains for a given period of time, between two steps in the conveying motion. On the other hand however, that advantage is achieved at the expense of the disadvantage that, when more than two prints or impressions are to be applied to the article in the one or more printing stations following the first printing station, the articles must first be realigned so that the individual prints to be applied thereto are in the correct position relative to each other.